Retirement Pay Question

[QuiGonJohn]

Can someone explain a couple things to me? So we get our check, supposedly at the end of each month. So, is that our retirement benefit for the month that is ending. Ex.: my current RAS says Pay Due as of 12/30/2022. So is that for this Dec.? Now, how come the amount changes from the prior 11 months of this year? It would seem to me that the pay raise is for 2023, so it should first be paid in the check at the end of Jan 2023. I've been getting retired pay a couple years now and this continues to baffle me. Also, I think at least a couple times, some of the figures changed from the check at the end of Dec, compared with the next check, end of Jan. Those changes are usually small, a dollar or less. Why? Thanks.